Stable Isotope clues to the formation and evolution of refrozen melt ponds on Arctic Sea ice.

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 123(12), (2018): 8887-8901, doi:10.1029/2018JC013797.Sea ice is one of the determining parameters of the climate system. The presence of melt ponds on the surface of Arctic sea ice plays a critical role in the mass balance of sea ice. A total of nine cores was collected from multiyear ice refrozen melt ponds and adjacent hummocks during the 2015 Arctic Sea State research cruise. The depth profiles of water isotopes, salinity, and ice texture for these sea ice cores were examined to provide information about the development of refrozen melt ponds and water balance generation processes, which are otherwise difficult to acquire. The presence of meteoric water with low oxygen isotope values as relatively thin layers indicates melt pond water stability and little mixing during formation and refreezing. The hydrochemical characteristics of refrozen melt pond and seawater depth profiles indicate little snowmelt enters the upper ocean during melt pond refreezing. Due to the seasonal characters of deuterium excess for Arctic precipitation, water balance calculations utilizing two isotopic tracers (oxygen isotope and deuterium excess) suggest that besides the melt of snow cover, the precipitation input in the melt season may also play a role in the evolution of melt ponds. The dual‐isotope mixing model developed here may become more valuable in a future scenario of increasing Arctic precipitation. The layers of meteoric origin were found at different depths in the refrozen melt pond ice cores. Surface topography information collected at several core sites was examined for possible explanations of different structures of refrozen melt ponds.The coauthors (S. F. A., S. S., T. M., and B. W.) wish to thank the other DRI participants and the Captain and crew of the Sikuliaq's October 2015 cruise for their assistance in the sample collections analyzed in the paper. Jim Thomson (Chief Scientist), Scott Harper (ONR Program Manager), and Martin Jeffries (ONR Program Manager) are particularly acknowledged for their unwavering assistance and leadership during the 5 years of the SeaState DRI. We thank Guy Williams for production of the aerial photo mosaic. Funding from the Office of Naval Research N00014‐13‐1‐0435 (S. F. A. and B. W.), N00014‐13‐1‐0434 (S. S.), and N00014‐13‐1‐0446 (T. M.) supported this research through grants to UTSA, UColorado, and WHOI, respectively. This project was also funded (in part) by the University of Texas at San Antonio, Office of the Vice President for Research (Y. G. and S. F. A.). Data for the stable isotope mixing models used in this study are shown in supporting information Tables S1–S3.2019-05-1

Spatial distribution and ecological risk assessment of heavy metals in alpine grasslands of the Zoige Basin, China

Heavy metals elements are not only related to the functions of ecosystems but also affect human health. To understand the characteristics of heavy metals in the topsoil of the Zoige alpine basin, a total of 252 grass and topsoil samples were collected in May and September 2014. The results showed that only Cd and Pb highly exceeded their background values (BV); in May and September, Cd was 2.02- and 1.55-fold higher than its BV, respectively, and Pb was 2.35- and 2.17-fold above its BV, respectively. The sources of Cd and Pb were homologous. In addition, the comprehensive potential ecological risk index was less than 150, indicating that heavy metal pollution in the study area is currently low. The spatial interpolation indicated that Cd and Pb pollution might be related to tourism and transportation, but the low biological absorption coefficient for all heavy metals showed that heavy metal absorption ability of forage was low and would not impact yak breeding. Finally, the soil was lightly contaminated by Cd and Pb due to the rapid development of the animal husbandry and tourism. The spatial variation of heavy metal in the basin is dominated by structural factors, and the random factors also have an effect on spatial distribution of As, Cd, Cu and Ni. The random factors such as overgrazing can exert an influence on physical structure and the circulation of nutrient substances of meadow soil through livestock grazing and trampling, ultimately affecting the content and distribution of soil heavy metals

Enhancement of electrical and thermal properties of graphene by aligned carbon nanotubes

Abstract In order to explore the composite effects of graphene (GR) and carbon nanotubes (CNTs), GR/CNTs aerogels and GR/CNTs coatings were fabricated. Aligned carbon nanotubes (ACNTs) and twining carbon nanotubes (TCNTs) were comparatively examined by integrating them with graphene, which has seldom been studied in detail. Freeze drying was novelly adopted to retain the liquid distribution in GR/CNTs mixture. Fourier Transform Infrared Spectroscopy (FTIR) analysis demonstrated that OH group and carboxylic acid groups were effectively induced onto CNTs via chemical modification. Scanning electron microscopy (SEM) showed that ACNTs achieved better dispersion and homogeneity in graphene than TCNTs. GR/CNTs hybrid composite with various loading of ACNTs or TCNTs were examined by electrical/thermal conductivity tests and practically evaluated for thermal management in LEDs. Results revealed that the electrical and thermal properties of graphene can be dramatically enhanced by the proper addition of ACNTs due to the formation of effective conductive bridges. The GR/ACNTs aerogel with 10 wt% ACNTs attained a high electrical conductivity of 2.08?×?104 S m?1, elevated to 2.76?×?104 S m?1 after annealing treatment. The eco-friendly and low-cost GR/ACNTs coating with 10 wt% ACNTs prominently reduced the operating temperature of LEDs by 8.6 °C, acting as potential thermal management materials in practical applications

Investigation of water quality and groundwater flow in a karst watershed in Blanco County, Texas

In any natural system, environmental and geomorphic responses are more extreme and frequent when caused or affected by human activities. Karst aquifers differ from other aquifer types in that they are composed of complex matrix, fracture, and conduit porosities. As valuable resources for societies and ecosystems, karst aquifers are highly vulnerable to pollution and must be well studied for proper protection.This study combines ongoing monitoring data with hydrochemistry data from sampling sites within the Honeycut Hollow Creek Watershed, Blanco County, Texas. Flow measurements revealed that the discharge of Honeycut Creek Spring does not respond to local precipitation. The wettest September in 2018 in recorded history in southcentral Texas resulted in minimum discharge, which is one order of magnitude lower than the discharge recorded from April 2017. During low flow conditions, the salinity of spring water is higher with elevated levels of nitrate and higher concentrations of other ions, especially sulfate.There has been little variation for water isotopes of Honeycut Creek Spring during 2017–2019, which may demonstrate relatively long residence time of groundwater and a deep flow path. This could also explain why the discharge of Honeycut Spring does not respond to local precipitation. The deuterium excess values of these spring water samples are close to 10‰, which may indicate little evaporation during precipitation and groundwater movement.These investigations aim to reveal the relationship between water quality of springs and local geoenvironmental conditions, evaluate the impact of long-term climate variations and wet and dry conditions on water quality, identify possible sources of nitrate among sampling sites, and ultimately generate a baseline model for a better understanding on how the karst aquifer responds to recharge events and potential contamination

Micro-Study of the Evolution of Rural Settlement Patterns and Their Spatial Association with Water and Land Resources: A Case Study of Shandan County, China

The balance between population and water and land resources is an important part of regional sustainable development. It is also significant for the ecological civilization in China and can help solve the Three Rural Issues (agriculture, countryside and farmers) in China. The Silk Road Economic Belt and Maritime Silk Road in twenty-first Century Strategy have brought new opportunities for the Hexi Corridor, which is facing challenges in the sustainable development of rural settlements. In this paper, we analyzed the temporal-spatial differentiation of rural settlement patterns in Shandan County of Hexi Corridor and studied the spatial association between rural settlements and water-land resources. Results show that the total area of rural settlement patches (CA), the number of rural settlement patches (NP), the mean patch area (MPS), the maximum patch areas (MAXP), the minimum patch areas (MINP) and the density of rural settlement patches (PD) changed more rapidly from 1998 to 2008 than from 2008 to 2015. In the second period, the indices mentioned before did not change significantly. The kernel density of rural settlements is basically consistent in three periods. Rural settlements mainly distribute along major roads and the hydrographic network and the kernel density of rural settlements decreases in the direction away from these roads and the hydrographic network. In addition, rural settlements in Shandan County are densely distributed in some regions and sparsely distributed in other regions. The dispersion degree of rural settlements increased from 1998 to 2008 and tended to be stable after 2008. These lead to the dispersion, hollowing and chaos of rural settlements in Shandan County. The spatial distribution of rural settlements in Shandan County is closely related to that of cultivated land and the hydrographic network. Our results might provide a theoretical basis for the reasonable utilization of water and land resources in Shandan County. Ultimately, a balance between population and water and land resources and regional sustainable development can be achieved

Isolation, Purification and Characterization of β-Glucosidase from Cassava Roots

The isolation, purification and enzymatic properties of β-glucosidase from cassava roots were studied. The crude enzyme extract was obtained from cassava roots with buffer solution, and the activity of crude enzyme was 9.37 U/g cassava dry weight. Purified by acetone precipitation, ion exchange chromatography and gel filtration chromatography, β-glucosidase activity was 1.14 U/g cassava dry weight, purified β-glucosidase purity increased by 14.62 times, the total activity recovery was 12.14%, the molecular weight of β-glucosidase was about 70 kDa. The Km and Vmax of the enzyme were 3.60 mmol/L and 12.36 µmol/(min·mg protein) respectively. The optimum pH was 7.0, and it was stable when the pH was between 6.0 and 8.0. It had good stability within 40 ℃, and 81.78% enzyme activity remained after 30 days at 4 ℃. Mn2+ and K+ promoted the enzyme to a certain extent. Al3+, Cu2+, Mg2+, Zn2+, Ca2+, Ba2+, Na+, urea and SDS had no significant effect on the enzyme activity (P>0.05). Fe3+, Fe2+, Ag+ and EDTA all inhibited the enzyme activity to varying degrees, among which Ag+ had the strongest inhibitory effect. The results can provide theoretical basis for the application of β-glucosidase in cassava roots in the future

Operation Optimization in a Smart Micro-Grid in the Presence of Distributed Generation and Demand Response

With the application of distributed generation and the development of smart grid technology, micro-grid, an economic and stable power grid, tends to play an important role in the demand side management. Because micro-grid technology and demand response have been widely applied, what Demand Response actions can realize the economic operation of micro-grid has become an important issue for utilities. In this proposed work, operation optimization modeling for micro-grid is done considering distributed generation, environmental factors and demand response. The main contribution of this model is to optimize the cost in the context of considering demand response and system operation. The presented optimization model can reduce the operation cost of micro-grid without bringing discomfort to the users, thus increasing the consumption of clean energy effectively. Then, to solve this operational optimization problem, genetic algorithm is used to implement objective function and DR scheduling strategy. In addition, to validate the proposed model, it is employed on a smart micro-grid from Tianjin. The obtained numerical results clearly indicate the impact of demand response on economic operation of micro-grid and development of distributed generation. Besides, a sensitivity analysis on the natural gas price is implemented according to the situation of China, and the result shows that the natural gas price has a great influence on the operation cost of the micro-grid and effect of demand response